An interactive display device, such as surface computing device, may be configured to allow a user to interact with the device via a touch-interactive display surface, rather than, or in addition to, peripheral input and output devices such as keyboards, cursor control devices, and monitors. A variety of touch-sensing mechanisms may be used to sense touch in an interactive display device, including but not limited to capacitive, resistive, and optical mechanisms. An optical touch-sensing mechanism may utilize one or more cameras to acquire images of the touch-sensitive surface, thereby allowing the detection of fingers and other objects touching the touch-sensitive surface in such images.